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Particular features and quenching mechanisms of exciton luminescence of water-soluble nanocomposites that are formed as a result of the interaction of surface charged semiconductor quantum dots (QDs) CdSe/ZnS ( d = 2.8 nm) and cationic porphyrins (HTMPyrP and ZnTMPyrP) have been studied theoretically and experimentally. It has been found that, in CdSe/ZnS⊕Porphyrin conjugates, there occurs long-range inductive resonance electronic excitation energy transfer from surface modified (with thioglycolic or mercaptoundecanoic acid) QDs to porphyrins, which is accompanied by quenching of the exciton luminescence of QDs and an increase in the fluorescence intensity of porphyrin. It has been shown that, when mercaptoundecanoic acid is used as a QD shell, the QD luminescence quenching efficiency by porphyrins follows the Förster-Galanin theory and depends on the overlap integral between the CdSe/ZnS luminescence band and the absorption spectra of free-base porphyrin HTMPyrP and its metal complex ZnTMPyrP. It has been revealed that, as the QDs ↔ Zn-porphyrin intercenter distance decreases from 39.1 (mercaptoundecanoic acid) to 30.1), a considerable QD luminescence quenching is observed; however, the energy transfer efficiency substantially decreases, from 55% in the former case to 23% in the latter one. Based on the spectral-luminescent data and quantum-chemical calculations, it has been found that the chemical change of HTMPyrP in the structure of the complex with CdSe/ZnS QDs passivated by thioglycolic or mercaptoundecanoic acid is caused by the formation of a metal complex ZnTMPyrP. Based on calculations of the redox-potentials, it has been concluded that the low luminescence quantum yield of CdSe/ZnS QDs passivated by residues of mercaptocarboxylic acids S(CH)COO and its dependence on the number of CH groups are related to the possibility of photoinduced electron transfer from the HOMO of passivating molecules to QDs (QD* ⇐ S(CH) nCOO hole transfer). It has been shown that the quenching of the exciton luminescence of QDs in heterogeneous structures CdSe/ZnS(thioglycolic acid)⊕ZnTMPyrP, which is complementary to the energy transfer, can be caused by the photoinduced electron transfer that involves the participation of the LUMO of the ZnTMPyrP molecule (QD* ⇒ ZnTMPyrP). [ABSTRACT FROM AUTHOR]

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO-N and CO-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296-700 K using a frequency-stabilized tunable CO laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 100-001 transition in CO molecules. [ABSTRACT FROM AUTHOR]

New absorption bands due to spin-forbidden transitions from the ground state to excited triplet states are found at 295 K in the near-IR absorption spectra of a number of Cu(II) complexes of octaethylporphyrin (OEP) that differ in the nature, number, and position of their side substituents. The frequency distribution, number, and nature of these transitions are analyzed using computer decomposition of complex contours into Gaussian components and additional data from the phosphorescence and phosphorescence excitation spectra (295–77 K). The d-π exchange integrals, determining the energy splitting ΔE = E(2T1) – E(4T1) in the compounds under study, are calculated on the basis of the experimental data obtained. It is shown that, in addition to the formally spin-allowed 2S0→2T1 transition (λmax = 833 nm), the absorption spectrum of the nonplanar CuOETPP molecule at 295 K exhibits the low-intensity spin-forbidden 2S0→4T1 transition (λmax = 937 nm). For this compound at 77 K, phosphorescence from the 4T1 state is observed (λmax = 955 nm), with a quantum yield equal to φPh = 0.0015 and a decay time amounting to τPh = 190 ns. For the CuOEP–Ph(o-NO2) molecule, which contains the electron-acceptor nitro group, direct absorption from the ground state S0 to a charge transfer (CT) state (λmax = 845 nm) is observed at 295 K. The extinction coefficient of this absorption and the energy of the CT state are determined. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]